Ammonia is a promising clean and sustainable energy carrier, yet challenges persist in achieving stable combustion, particularly concerning poor ignition quality and elevated NOx emissions. Recent research suggests that the Moderate or Intense Low-oxygen Dilution (MILD) regime could address these challenges for ammonia combustion. This study aims to optimize the MILD regime using non-equilibrium plasma discharges, specifically nanosecond repetitive pulsed discharges (NRPD). While the beneficial effects of NRPD on ammonia chemistry have been demonstrated in traditional applications, their impact under the highly diluted conditions characteristic of the MILD regime remains unexplored. This numerical study employs a detailed two-temperature model to investigate the effects of pulsed discharges in ammonia/air mixtures, simulating conditions representative of the MILD regime. The research comprehensively explores the selection of optimal discharge settings and examines plasma effects on various parameters, including ignition delay time, flammability limit, radical production, and emissions. Equivalence ratios ranging from 0.2 to 2 and dilution levels up to 2.5% O are considered in this investigation. Results indicate that NRPD show a notable benefit by enlarging fuel-lean and fuel-rich stability limits, promising enhanced operational flexibility. Examining OH radicals and NOx emissions underscored a consistent plasma-driven mechanism, reducing emissions, also in the MILD regime.
{"title":"Nanosecond pulsed plasma-assisted MILD combustion of ammonia","authors":"Georgios Rekkas-Ventiris, Pino Sabia, Giancarlo Sorrentino, Aurélie Bellemans","doi":"10.1016/j.proci.2024.105384","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105384","url":null,"abstract":"Ammonia is a promising clean and sustainable energy carrier, yet challenges persist in achieving stable combustion, particularly concerning poor ignition quality and elevated NOx emissions. Recent research suggests that the Moderate or Intense Low-oxygen Dilution (MILD) regime could address these challenges for ammonia combustion. This study aims to optimize the MILD regime using non-equilibrium plasma discharges, specifically nanosecond repetitive pulsed discharges (NRPD). While the beneficial effects of NRPD on ammonia chemistry have been demonstrated in traditional applications, their impact under the highly diluted conditions characteristic of the MILD regime remains unexplored. This numerical study employs a detailed two-temperature model to investigate the effects of pulsed discharges in ammonia/air mixtures, simulating conditions representative of the MILD regime. The research comprehensively explores the selection of optimal discharge settings and examines plasma effects on various parameters, including ignition delay time, flammability limit, radical production, and emissions. Equivalence ratios ranging from 0.2 to 2 and dilution levels up to 2.5% O are considered in this investigation. Results indicate that NRPD show a notable benefit by enlarging fuel-lean and fuel-rich stability limits, promising enhanced operational flexibility. Examining OH radicals and NOx emissions underscored a consistent plasma-driven mechanism, reducing emissions, also in the MILD regime.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141551160","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
During NH/H combustion, reactant jets entrain the burnt gas, resulting in a combustion zone diluted with HO. Therefore, the effect of HO dilution on NO formation should be carefully examined. In this study, NH/H oxidation with N and HO dilutions was investigated in a jet-stirred reactor (JSR). A systematic experimental analysis was conducted to investigate the effects of different factors, including temperature (), equivalence ratio (Φ), and HO volume fraction (). A numerical simulation was conducted using a modified mechanism to interpret the measured results and examine the kinetic pathways. NO formation is enhanced as increases but inhibited as Φ increases The effect of HO dilution on NO formation is related to and Φ. Under fuel-lean conditions, NO generation is hindered by HO dilution. NO formation is reduced by 43 % at = 1375 K and Φ = 0.5. In contrast, under fuel-rich conditions (Φ > 1), HO dilution promotes NO formation at high temperatures (e.g., > 1300 K at Φ = 2.5) The NO concentration peaks at approximately 1250 K in cases of N dilution, and 25 % HO dilution increases the of the peak NO concentration by approximately 100 K. At 1375 K, the promoting effect of HO on NO generation is significant at = 10 %. This study provides new insights into the effect of HO dilution on NO formation characteristics during NH/H oxidation.
在 NH/H 燃烧过程中，反应物喷流会夹带燃烧气体，导致燃烧区被 HO 稀释。因此，应仔细研究 HO 稀释对 NO 形成的影响。本研究在喷射搅拌反应器（JSR）中研究了 NH/H 氧化与 N 和 HO 稀释的关系。通过系统的实验分析，研究了温度（）、当量比（Φ）和 HO 体积分数（）等不同因素的影响。为了解释测量结果和研究动力学路径，使用修改过的机理进行了数值模拟。HO 稀释对 NO 生成的影响与 Φ 有关。在缺乏燃料的条件下，HO 稀释会阻碍 NO 的生成。在 = 1375 K 和 Φ = 0.5 时，NO 的形成减少了 43%。与此相反，在燃料丰富的条件下（Φ > 1），HO 稀释在高温下（例如，Φ = 2.5 时 > 1300 K）促进了 NO 的生成。在 N 稀释的情况下，NO 浓度在大约 1250 K 时达到峰值，25 % 的 HO 稀释使 NO 浓度峰值提高了大约 100 K。这项研究为了解 HO 稀释对 NH/H 氧化过程中 NO 生成特性的影响提供了新的视角。
{"title":"Effect of H2O dilution on NOx emissions from the oxidation of NH3/H2 fuel mixture","authors":"Guodong Shi, Pengfei Li, Zhaohui Liu, Bassam Dally","doi":"10.1016/j.proci.2024.105407","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105407","url":null,"abstract":"During NH/H combustion, reactant jets entrain the burnt gas, resulting in a combustion zone diluted with HO. Therefore, the effect of HO dilution on NO formation should be carefully examined. In this study, NH/H oxidation with N and HO dilutions was investigated in a jet-stirred reactor (JSR). A systematic experimental analysis was conducted to investigate the effects of different factors, including temperature (), equivalence ratio (Φ), and HO volume fraction (). A numerical simulation was conducted using a modified mechanism to interpret the measured results and examine the kinetic pathways. NO formation is enhanced as increases but inhibited as Φ increases The effect of HO dilution on NO formation is related to and Φ. Under fuel-lean conditions, NO generation is hindered by HO dilution. NO formation is reduced by 43 % at = 1375 K and Φ = 0.5. In contrast, under fuel-rich conditions (Φ > 1), HO dilution promotes NO formation at high temperatures (e.g., > 1300 K at Φ = 2.5) The NO concentration peaks at approximately 1250 K in cases of N dilution, and 25 % HO dilution increases the of the peak NO concentration by approximately 100 K. At 1375 K, the promoting effect of HO on NO generation is significant at = 10 %. This study provides new insights into the effect of HO dilution on NO formation characteristics during NH/H oxidation.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141551158","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-01DOI: 10.1016/j.proci.2024.105292
Kevin Gleason, Francesco Carbone, Alessandro Gomez
The challenge of soot emission persists in combustion research due to the complexities of tracking the crucial stages of growth from fuel to soot nuclei and ultimately mature particles. Studying soot formation in flames often requires a sophisticated approach, involving detailed measurements of gaseous soot precursors and soot particles using multiple complementary diagnostics. On the other end of the spectrum of studies are simpler methods that capture the sooting tendency using a single index, akin to the cetane number in compression ignition engines and the octane number in spark ignition engines. This article seeks a middle ground, aiming to the soot production rate while maintaining the simplicity of single-index characterizations. The approach involves establishing counterflow diffusion flames, measuring soot volume fraction through pyrometry, and accurately computing velocity and temperature profiles using a commercial code. These data allow for the quantification of the production rate from the soot governing equation. The methodology is applied to counterflow ethylene diffusion flames to examine the temperature dependence of the soot production rate across peak temperatures varying by several hundred degrees and pressures in the 1–32 atm range. The soot production rate per unit flame area falls within the range of 10–10 g/(cms) range and, when normalized with respect to the carbon flux, it ranges between 10 and nearly 10. On a logarithmic scale, it linearly correlates with the peak temperature at a fixed pressure. Although this study deals only with flames of ethylene, the approach can be generalized to any fuel. The resulting database should be valuable not only for industry practitioners but also to the scientific community for the global validation of detailed soot models.
{"title":"An easy but quantitative assessment of soot production rate and its dependence on temperature and pressure","authors":"Kevin Gleason, Francesco Carbone, Alessandro Gomez","doi":"10.1016/j.proci.2024.105292","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105292","url":null,"abstract":"The challenge of soot emission persists in combustion research due to the complexities of tracking the crucial stages of growth from fuel to soot nuclei and ultimately mature particles. Studying soot formation in flames often requires a sophisticated approach, involving detailed measurements of gaseous soot precursors and soot particles using multiple complementary diagnostics. On the other end of the spectrum of studies are simpler methods that capture the sooting tendency using a single index, akin to the cetane number in compression ignition engines and the octane number in spark ignition engines. This article seeks a middle ground, aiming to the soot production rate while maintaining the simplicity of single-index characterizations. The approach involves establishing counterflow diffusion flames, measuring soot volume fraction through pyrometry, and accurately computing velocity and temperature profiles using a commercial code. These data allow for the quantification of the production rate from the soot governing equation. The methodology is applied to counterflow ethylene diffusion flames to examine the temperature dependence of the soot production rate across peak temperatures varying by several hundred degrees and pressures in the 1–32 atm range. The soot production rate per unit flame area falls within the range of 10–10 g/(cms) range and, when normalized with respect to the carbon flux, it ranges between 10 and nearly 10. On a logarithmic scale, it linearly correlates with the peak temperature at a fixed pressure. Although this study deals only with flames of ethylene, the approach can be generalized to any fuel. The resulting database should be valuable not only for industry practitioners but also to the scientific community for the global validation of detailed soot models.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141550979","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-01DOI: 10.1016/j.proci.2024.105391
Cooper Welch, Jannick Erhard, Hao Shi, Andreas Dreizler, Benjamin Böhm
This experimental study explores the pivotal role of thermodiffusive and hydrodynamic instabilities in shaping the early development of lean hydrogen flames within a spark-ignition engine. Utilizing high-speed planar laser-induced fluorescence of inert SO tracer gas, the flame front is visualized to scrutinize the lean H flame propagation in an optically accessible single-cylinder spark-ignition engine operating at 800rpm and intake pressures of 0.4bar and 0.95bar. Comparisons between H/air and CH/air flames reveal minimal disparity in the statistical distributions of flame surface density under identical initial conditions. This suggests that, within the dynamic engine environment, the influences of thermodiffusive and hydrodynamic instabilities may be counteracted by competing factors, including turbulence and dynamic volume confinement. While traditional bomb calorimeter experiments and laminar simulations provide insights into hydrogen flame evolution, their observed effects may be less pronounced in real-world applications where turbulence and flame-wall interactions play a major role. However, by significantly reducing the equivalence ratio, the observed increase in underscores that the cumulative effects of flame instabilities become notable under extremely lean conditions, even within the dynamic engine environment. This study marks a significant step in gaining new insights into the influence of flame instabilities on H-fueled spark-ignition engines. Finally, the elucidation of turbulence and flame-wall interactions in attenuating thermodiffusive instabilities presents a promising avenue for future research.
{"title":"An experimental investigation of lean hydrogen flame instabilities in spark-ignition engines","authors":"Cooper Welch, Jannick Erhard, Hao Shi, Andreas Dreizler, Benjamin Böhm","doi":"10.1016/j.proci.2024.105391","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105391","url":null,"abstract":"This experimental study explores the pivotal role of thermodiffusive and hydrodynamic instabilities in shaping the early development of lean hydrogen flames within a spark-ignition engine. Utilizing high-speed planar laser-induced fluorescence of inert SO tracer gas, the flame front is visualized to scrutinize the lean H flame propagation in an optically accessible single-cylinder spark-ignition engine operating at 800rpm and intake pressures of 0.4bar and 0.95bar. Comparisons between H/air and CH/air flames reveal minimal disparity in the statistical distributions of flame surface density under identical initial conditions. This suggests that, within the dynamic engine environment, the influences of thermodiffusive and hydrodynamic instabilities may be counteracted by competing factors, including turbulence and dynamic volume confinement. While traditional bomb calorimeter experiments and laminar simulations provide insights into hydrogen flame evolution, their observed effects may be less pronounced in real-world applications where turbulence and flame-wall interactions play a major role. However, by significantly reducing the equivalence ratio, the observed increase in underscores that the cumulative effects of flame instabilities become notable under extremely lean conditions, even within the dynamic engine environment. This study marks a significant step in gaining new insights into the influence of flame instabilities on H-fueled spark-ignition engines. Finally, the elucidation of turbulence and flame-wall interactions in attenuating thermodiffusive instabilities presents a promising avenue for future research.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141551159","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-01DOI: 10.1016/j.proci.2024.105223
Juan Camilo Giraldo Delgado, Khalid Alhazmi, Inna Gorbatenko, Deanna A. Lacoste, S. Mani Sarathy
Thermoacoustic instabilities pose challenges for several combustion applications, such as rockets, ramjets, aeroengines and boilers. The mitigation of these instabilities requires decoupling unsteady heat release and acoustics of the system. While existing strategies rely in theoretical approaches, this paper introduces a fully data-driven approach for modelling and control of systems with sustained pressure oscillations. A nonlinear autoregressive model (NARX) with neural networks was trained on experimental data obtained from a laminar premixed flame exhibiting a thermoacoustic instability at 166 Hz. The NARX model showed good prediction capabilities using closed-loop measurements. Furthermore, given the limitations that traditional control techniques face for nonlinear systems, this work explores the application of offline reinforcement learning for tuning the parameters of a phase-shift controller. The reinforcement learning model is trained using the NARX model as the environment. The study demonstrates the potential of reinforcement learning for control of thermoacoustic instabilities and shows that the parameters suggested by the model fall in the range where the thermoacoustic instability can be reduced.
{"title":"Controlling thermoacoustic instability of a laminar premixed flame with deep reinforcement learning and neural autoregressive models","authors":"Juan Camilo Giraldo Delgado, Khalid Alhazmi, Inna Gorbatenko, Deanna A. Lacoste, S. Mani Sarathy","doi":"10.1016/j.proci.2024.105223","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105223","url":null,"abstract":"Thermoacoustic instabilities pose challenges for several combustion applications, such as rockets, ramjets, aeroengines and boilers. The mitigation of these instabilities requires decoupling unsteady heat release and acoustics of the system. While existing strategies rely in theoretical approaches, this paper introduces a fully data-driven approach for modelling and control of systems with sustained pressure oscillations. A nonlinear autoregressive model (NARX) with neural networks was trained on experimental data obtained from a laminar premixed flame exhibiting a thermoacoustic instability at 166 Hz. The NARX model showed good prediction capabilities using closed-loop measurements. Furthermore, given the limitations that traditional control techniques face for nonlinear systems, this work explores the application of offline reinforcement learning for tuning the parameters of a phase-shift controller. The reinforcement learning model is trained using the NARX model as the environment. The study demonstrates the potential of reinforcement learning for control of thermoacoustic instabilities and shows that the parameters suggested by the model fall in the range where the thermoacoustic instability can be reduced.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141550995","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-01DOI: 10.1016/j.proci.2024.105215
Peng Liu, You Zhang, Junjun Guo, Adamu Alfazazi, Carson Chu, Raul Serrano-Bayona, Faruk Aydin, Et-touhami Es-sebbar, Hong G. Im, Bassam Dally, Xiang Gao, William L. Roberts
Autothermal reforming (ATR) of methane is a promising technology for low-carbon H production due to its high CO capture efficiency (>95 %) and cost advantage. Especially, reforming CO+CH greenhouse gases to valuable CO+H gases is a feasible solution for carbon-neutral energy systems. Flame temperature, reforming gas composition and concentration, and soot loading are major factors determining the efficiency of H production in the subsequent catalyst region. In this study, the effects of CO/CH ratio on the profiles of temperature, OH radical, light gas products, large polycyclic aromatic hydrocarbons (PAHs), and soot were investigated for CH-CO-O laminar inverse diffusion flames near ATR conditions, using the combined non-intrusive and intrusive diagnostic methods. Pure O as oxidizer was fed through the central nozzle of the burner surrounded by CH fuel diluted with CO. The experimental results revealed that the formation of soot and PAHs was greatly suppressed with a higher CO/CH ratio. The PAHs and soot loading followed exponential function as CO/CH mole ratio, regardless of pressure, O mole fraction, and burner size. The flame height was found to increase linearly with CO dilution, and the high temperature region (> 1000 K) shifts downstream. The H production decreased with CO/CH ratio, while CO production is less sensitive to CO dilution. The importance of radical species during soot formation is confirmed based on the comprehensive data set. Moreover, five well-known chemical-kinetic mechanisms were evaluated against experimental datasets. The comparisons indicate that the flame temperature and concentration trends of investigated species are well predicted, but future work is needed to improve the prediction accuracy of amplitude and spatial distribution, especially for CH, PAHs and soot. The reported experiment and simulation results can provide valuable guidance for ATR model validation, development, reduction, and application.
甲烷的自热转化（ATR）具有较高的二氧化碳捕集效率（>95%）和成本优势，是一种前景广阔的低碳氢气生产技术。特别是，将 CO+CH 温室气体转化为有价值的 CO+H 气体是碳中和能源系统的可行解决方案。火焰温度、重整气体成分和浓度以及烟尘负荷是决定后续催化剂区 H 生产效率的主要因素。本研究采用非侵入式和侵入式相结合的诊断方法，研究了在 ATR 条件下，CH-CO-O 层流反向扩散火焰中 CO/CH 比率对温度、OH 自由基、轻气体产物、大型多环芳烃 (PAH) 和烟尘的影响。纯 O 作为氧化剂通过燃烧器的中央喷嘴送入，周围是用 CO 稀释的 CH 燃料。实验结果表明，CO/CH 比值越高，烟尘和多环芳烃的形成就越受抑制。多环芳烃和烟尘的负荷随 CO/CH 摩尔比呈指数函数变化，与压力、O 摩尔分数和燃烧器大小无关。火焰高度随着 CO 的稀释而线性增加，高温区（> 1000 K）向下游移动。H 生成量随 CO/CH 比率的增加而减少，而 CO 生成量对 CO 稀释的敏感性较低。基于综合数据集，证实了自由基物种在烟尘形成过程中的重要性。此外，还根据实验数据集评估了五种著名的化学动力学机制。比较结果表明，所研究物种的火焰温度和浓度趋势得到了很好的预测，但还需要进一步提高对振幅和空间分布的预测精度，尤其是对 CH、PAHs 和烟尘的预测精度。所报告的实验和模拟结果可为 ATR 模型的验证、开发、缩减和应用提供有价值的指导。
{"title":"Characterization of CH4-CO2-O2 diffusion flames near autothermal reforming condition","authors":"Peng Liu, You Zhang, Junjun Guo, Adamu Alfazazi, Carson Chu, Raul Serrano-Bayona, Faruk Aydin, Et-touhami Es-sebbar, Hong G. Im, Bassam Dally, Xiang Gao, William L. Roberts","doi":"10.1016/j.proci.2024.105215","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105215","url":null,"abstract":"Autothermal reforming (ATR) of methane is a promising technology for low-carbon H production due to its high CO capture efficiency (>95 %) and cost advantage. Especially, reforming CO+CH greenhouse gases to valuable CO+H gases is a feasible solution for carbon-neutral energy systems. Flame temperature, reforming gas composition and concentration, and soot loading are major factors determining the efficiency of H production in the subsequent catalyst region. In this study, the effects of CO/CH ratio on the profiles of temperature, OH radical, light gas products, large polycyclic aromatic hydrocarbons (PAHs), and soot were investigated for CH-CO-O laminar inverse diffusion flames near ATR conditions, using the combined non-intrusive and intrusive diagnostic methods. Pure O as oxidizer was fed through the central nozzle of the burner surrounded by CH fuel diluted with CO. The experimental results revealed that the formation of soot and PAHs was greatly suppressed with a higher CO/CH ratio. The PAHs and soot loading followed exponential function as CO/CH mole ratio, regardless of pressure, O mole fraction, and burner size. The flame height was found to increase linearly with CO dilution, and the high temperature region (> 1000 K) shifts downstream. The H production decreased with CO/CH ratio, while CO production is less sensitive to CO dilution. The importance of radical species during soot formation is confirmed based on the comprehensive data set. Moreover, five well-known chemical-kinetic mechanisms were evaluated against experimental datasets. The comparisons indicate that the flame temperature and concentration trends of investigated species are well predicted, but future work is needed to improve the prediction accuracy of amplitude and spatial distribution, especially for CH, PAHs and soot. The reported experiment and simulation results can provide valuable guidance for ATR model validation, development, reduction, and application.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141550996","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-01DOI: 10.1016/j.proci.2024.105256
Kihun Moon, Richard Martin, Bruno Schuermans, Nicolas Noiray
Understanding the response of multi-jet turbulent hydrogen-air flames to acoustic forcing is key for the development of future carbon-neutral gas turbine combustors. In this paper, we present flame transfer functions (FTFs) deduced from burner and flame transfer matrices obtained with acoustic measurements for fully-premixed (FP) and technically-premixed (TP) conditions, in conjunction with their analytical models. The matrix burner used in this study produces an array of sixteen turbulent lean hydrogen-air jet flames. Its acoustic transfer matrix is analytically modeled, with experimental validation. It exhibits a significant frequency dependence due to the non-compactness of the burner with respect to the acoustic wavelength considered. Our results show that the conical jet-stabilized flames have a typical low-pass filter behavior in the FP case, while in the TP case, they exhibit a frequency dependent gain modulation originating from the combination of mass flow and equivalence ratio oscillations. Using distributed time delay (DTD) models, we identify the dominant disturbances controlling the FTF data measured at different equivalence ratios and bulk velocities, and show that they can be well collapsed by using the associated Strouhal numbers. To unravel the smooth transition of FTF between the FP and TP cases, staging of the fuel is employed in the present study. We demonstrate that the features of the FTFs for staging conditions ranging from FP to TP are strongly correlated with the fuel staging ratio and can be well reproduced by a linear superposition of the FTFs of the pure FP and TP cases.
{"title":"Transfer functions of lean fully- and technically-premixed jet-stabilized turbulent hydrogen flames","authors":"Kihun Moon, Richard Martin, Bruno Schuermans, Nicolas Noiray","doi":"10.1016/j.proci.2024.105256","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105256","url":null,"abstract":"Understanding the response of multi-jet turbulent hydrogen-air flames to acoustic forcing is key for the development of future carbon-neutral gas turbine combustors. In this paper, we present flame transfer functions (FTFs) deduced from burner and flame transfer matrices obtained with acoustic measurements for fully-premixed (FP) and technically-premixed (TP) conditions, in conjunction with their analytical models. The matrix burner used in this study produces an array of sixteen turbulent lean hydrogen-air jet flames. Its acoustic transfer matrix is analytically modeled, with experimental validation. It exhibits a significant frequency dependence due to the non-compactness of the burner with respect to the acoustic wavelength considered. Our results show that the conical jet-stabilized flames have a typical low-pass filter behavior in the FP case, while in the TP case, they exhibit a frequency dependent gain modulation originating from the combination of mass flow and equivalence ratio oscillations. Using distributed time delay (DTD) models, we identify the dominant disturbances controlling the FTF data measured at different equivalence ratios and bulk velocities, and show that they can be well collapsed by using the associated Strouhal numbers. To unravel the smooth transition of FTF between the FP and TP cases, staging of the fuel is employed in the present study. We demonstrate that the features of the FTFs for staging conditions ranging from FP to TP are strongly correlated with the fuel staging ratio and can be well reproduced by a linear superposition of the FTFs of the pure FP and TP cases.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141550980","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-01DOI: 10.1016/j.proci.2024.105346
Weitao Liu, Andreas Kronenburg, Jan Wilhelm Gärtner, Jonas Kirchmann, Thorsten Zirwes
Reliable soot predictions in turbulent flames remain challenging due to the need to use relatively large chemical mechanisms and the presence of slow kinetics of the soot species that necessitate the use of an advanced combustion sub-model but prevent tabulation for all species in particular for soot precursor species such as PAHs. The joint probability density function (PDF) approach offers a “model-free” closure for the chemical source term but its computational expense typically hinders the incorporation of detailed soot mechanisms. In this study, a sparse particle method called ‘Multiple Mapping Conditioning’ (MMC) is used. The number of stochastic particles can be reduced by almost two orders of magnitude and large-eddy simulations of a turbulent ethylene flame with a detailed sectional soot model become feasible. Predicted concentrations of gaseous species and temperature agree well with experimental data and indicate an accurate modelling of the turbulent mixing process and gas phase reactions by MMC-LES. MMC-LES with the detailed sectional soot model and a second MMC-LES using a two-equation model provide accurate predictions of the zones where soot is formed and capture the onset of oxidation very well. Simulated peak values of soot volume fraction differ depending on the model, with values being around three times too large for the two-equation model while the detailed sectional model gives very decent agreement everywhere except in the very rich region along the centreline where soot volume fraction are overpredicted by up to 50%. The sectional model yields reasonable results for the aggregate size distributions everywhere in the flame and also the primary particle sizes predicted by the two-equation model agree with expected values, but a quantitative assessment is difficult as corresponding measurements are not available.
{"title":"Sparse-Lagrangian MMC modelling of the Sandia ethylene sooting flame","authors":"Weitao Liu, Andreas Kronenburg, Jan Wilhelm Gärtner, Jonas Kirchmann, Thorsten Zirwes","doi":"10.1016/j.proci.2024.105346","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105346","url":null,"abstract":"Reliable soot predictions in turbulent flames remain challenging due to the need to use relatively large chemical mechanisms and the presence of slow kinetics of the soot species that necessitate the use of an advanced combustion sub-model but prevent tabulation for all species in particular for soot precursor species such as PAHs. The joint probability density function (PDF) approach offers a “model-free” closure for the chemical source term but its computational expense typically hinders the incorporation of detailed soot mechanisms. In this study, a sparse particle method called ‘Multiple Mapping Conditioning’ (MMC) is used. The number of stochastic particles can be reduced by almost two orders of magnitude and large-eddy simulations of a turbulent ethylene flame with a detailed sectional soot model become feasible. Predicted concentrations of gaseous species and temperature agree well with experimental data and indicate an accurate modelling of the turbulent mixing process and gas phase reactions by MMC-LES. MMC-LES with the detailed sectional soot model and a second MMC-LES using a two-equation model provide accurate predictions of the zones where soot is formed and capture the onset of oxidation very well. Simulated peak values of soot volume fraction differ depending on the model, with values being around three times too large for the two-equation model while the detailed sectional model gives very decent agreement everywhere except in the very rich region along the centreline where soot volume fraction are overpredicted by up to 50%. The sectional model yields reasonable results for the aggregate size distributions everywhere in the flame and also the primary particle sizes predicted by the two-equation model agree with expected values, but a quantitative assessment is difficult as corresponding measurements are not available.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141550978","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-01DOI: 10.1016/j.proci.2024.105413
Chao Tao, Chi Zhang, Qiang An, Xin Xue, Jianting Gao, Xingzhou Fan
This paper investigates the 3D distribution features of fuel, hot spots (HS), and velocity in a centrally staged swirl spray combustor using particle image velocimetry (PIV) and simultaneous fuel/OH planar laser induced fluorescence (PLIF) at an inlet pressure of 0.5 MPa and temperature of 500 K. The pilot and main stages of the combustor were supplied with RP-3 kerosene. Multiple spanwise slices of the combustor were imaged and the resultant data were used to perform 3D reconstruction of the aforementioned physical fields via an interpolation method. Through visualization of the HS in various spanwise and axial slices, as well as more quantitative analysis on the circumferentially averaged radial profiles, HS merging between the main and pilot stages was examined based on the extracted spatial trajectories. Three zones of HS evolution were identified, namely pre-merging, merging, and post-merging. In the pre-merging zone, the hot spots of the two stages exhibited independent growth. As transitioning to the merging zone, the pilot HS was gradually diverted by the pilot air jet and merged to the main HS. In the post-merging zone, the main HS was largely dominated by the unburned fuel jet cores from the main stage. These results show the importance of comprehensive analysis on the 3D characteristics of physical quantities in understanding the HS behavior. This study provides valuable experimental support for regulating HS within the primary combustion zone of centrally staged aero-engine combustors.
{"title":"3D distribution of hot spots affected by flow and spray in a centrally staged combustor","authors":"Chao Tao, Chi Zhang, Qiang An, Xin Xue, Jianting Gao, Xingzhou Fan","doi":"10.1016/j.proci.2024.105413","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105413","url":null,"abstract":"This paper investigates the 3D distribution features of fuel, hot spots (HS), and velocity in a centrally staged swirl spray combustor using particle image velocimetry (PIV) and simultaneous fuel/OH planar laser induced fluorescence (PLIF) at an inlet pressure of 0.5 MPa and temperature of 500 K. The pilot and main stages of the combustor were supplied with RP-3 kerosene. Multiple spanwise slices of the combustor were imaged and the resultant data were used to perform 3D reconstruction of the aforementioned physical fields via an interpolation method. Through visualization of the HS in various spanwise and axial slices, as well as more quantitative analysis on the circumferentially averaged radial profiles, HS merging between the main and pilot stages was examined based on the extracted spatial trajectories. Three zones of HS evolution were identified, namely pre-merging, merging, and post-merging. In the pre-merging zone, the hot spots of the two stages exhibited independent growth. As transitioning to the merging zone, the pilot HS was gradually diverted by the pilot air jet and merged to the main HS. In the post-merging zone, the main HS was largely dominated by the unburned fuel jet cores from the main stage. These results show the importance of comprehensive analysis on the 3D characteristics of physical quantities in understanding the HS behavior. This study provides valuable experimental support for regulating HS within the primary combustion zone of centrally staged aero-engine combustors.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141551157","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-01DOI: 10.1016/j.proci.2024.105448
Jiahao Wang, Marco A.B. Zanoni, Tarek L. Rashwan, José L. Torero, Jason I. Gerhard
Applied smoldering has been demonstrated as an efficient waste-to-energy approach for low heating value/high moisture content combustible waste materials. Therefore, smoldering can be used to extract energy from wastes that are not amenable to traditional thermochemical routes (e.g., using flaming-based incinerators). Nevertheless, understanding the process of smoldering-driven drying and its relationship to ignition and quenching within these smoldering systems is critical to determine the viability and economic feasibility of this approach. These interlinked phenomena are not well-understood. To address this knowledge gap, this study developed new analytical methods with a previous validated numerical model to establish a comprehensive framework to better understand ignition and the associated drying process. These new models accurately resolve the coupling between downward water migration, water phase change, and smoldering propagation in space and time, revealing how drying defines ignition. The relationship between residual water saturation () and drying time to enable ignition () was determined analytically to unveil the fundamental relationships between these variables. represents a critical limiting water saturation for smoldering ignition, which was found to be solely dependent on material properties rather than operational conditions (e.g., initial water saturation or packing height). In contrast, , is the critical drying time that enables ignition, which was shown to be significantly influenced by system heat losses and operational parameters. Conditions such as a slender reactor design, insufficient thermal insulation, and low heater power can substantially extend the required drying period – and lead to ignition failure at critical conditions. Furthermore, a four-zone ignition region was established and used to characterize the requirements for smoldering ignition. Overall, this study untangles interlinked phenomena and supports researchers and engineers in better understanding drying and its influence on ignition within applied smoldering systems.
{"title":"Smoldering ignition of wet combustible materials","authors":"Jiahao Wang, Marco A.B. Zanoni, Tarek L. Rashwan, José L. Torero, Jason I. Gerhard","doi":"10.1016/j.proci.2024.105448","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105448","url":null,"abstract":"Applied smoldering has been demonstrated as an efficient waste-to-energy approach for low heating value/high moisture content combustible waste materials. Therefore, smoldering can be used to extract energy from wastes that are not amenable to traditional thermochemical routes (e.g., using flaming-based incinerators). Nevertheless, understanding the process of smoldering-driven drying and its relationship to ignition and quenching within these smoldering systems is critical to determine the viability and economic feasibility of this approach. These interlinked phenomena are not well-understood. To address this knowledge gap, this study developed new analytical methods with a previous validated numerical model to establish a comprehensive framework to better understand ignition and the associated drying process. These new models accurately resolve the coupling between downward water migration, water phase change, and smoldering propagation in space and time, revealing how drying defines ignition. The relationship between residual water saturation () and drying time to enable ignition () was determined analytically to unveil the fundamental relationships between these variables. represents a critical limiting water saturation for smoldering ignition, which was found to be solely dependent on material properties rather than operational conditions (e.g., initial water saturation or packing height). In contrast, , is the critical drying time that enables ignition, which was shown to be significantly influenced by system heat losses and operational parameters. Conditions such as a slender reactor design, insufficient thermal insulation, and low heater power can substantially extend the required drying period – and lead to ignition failure at critical conditions. Furthermore, a four-zone ignition region was established and used to characterize the requirements for smoldering ignition. Overall, this study untangles interlinked phenomena and supports researchers and engineers in better understanding drying and its influence on ignition within applied smoldering systems.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141551156","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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